Gable top cartons have been known for the better part of the twentieth century. Their characteristic simplicity and resealability have helped to sustain their popularity as cartons for traditional liquid food products such as milk and juice, but in recent years they have been used for products ranging from ammunition to Epsom salts. Gable top cartons typically start out as generally rectangular carton blanks made of laminated paperboard or similar material. The carton blanks are provided with a number of creases to facilitate folding and forming the blank into a carton.
During decades of development, manufacturers of packaging machines have devised a variety of ways to form, fill and seal gable top cartons. Today, the most prevalent packaging machines for filling and sealing gable top cartons are adapted to receive the carton blank after it has been side sealed. The process of side sealing involves sealing opposite vertical edges of the carton blank together to form a polygonal (usually rectangular) sleeve. The sleeve is received on an indexable mandrel wheel which rotates the sleeve into respective positions where the end of the sleeve extending outwardly from the mandrel is folded and sealed to form the bottom of the carton.
After the carton bottom has been formed, it is removed from the mandrel and transported to a filling station where the carton is filled with product. Once the carton has been filled, the top of the carton is folded into the familiar gable top configuration and is heat sealed, thus completing the packaging process.
One example of a known packaging machine that operates generally in accordance with these principles is described in U.S. Pat. No. 3,789,746 to Martensson et al. Other examples of such packaging machines are described in U.S. Pat. No. 3,820,303 to Martensson et al., U.S. Pat. No. 4,759,171 to Bruveris et al., and U.S. Pat. No. 4,790,123 to Ljungstrom et al. These patents are hereby incorporated by reference.
Various mechanisms are known for sealing the fin at the gabled end of the gable top carton. One such mechanism is disclosed in U.S. Pat. No. 3,200,557 to Schwenk. In accordance with the teachings of that patent, the upper flap panels that form the gabled structure, including the fin, are first heated to allow the polyethylene coating on the cartons to soften. The carton is then transported to a position between two sealing jaws. The sealing jaws move toward one another and apply pressure to form and seal the fin.
As the sealing jaws move toward one another, it is possible for the opposed flaps that are perpendicular to the jaws to extend outward as opposed to inward toward the carton. This condition is known as "duckbilling" and renders the carton and its contents unusable.
Various mechanisms have been devised to reduce or eliminate such "duckbilling". One such mechanism is disclosed in U.S. Pat. No. 4,738,077 to Wakbayashi et al. The mechanism described in the '077 patent utilizes an inverted, V-shaped claw to pre-fold the opposed flaps at the gabled end of the carton. This pre-folding takes place at a processing station of the packaging machine that is disposed prior to the sealing station at which the fin is sealed.
Although such pre-folding of the opposed flaps may assist in reducing "duckbilling", the foregoing mechanism is not necessarily the most desirable solution to the problem. The prefolding occurs at a separate pre-folding station thus adding significant cost and bulk to the packaging machine. A more cost effective and efficient solution would be beneficial.